This is another example of the canonical problem I covered in an earlier post. Looking up the link information for msn.com and www.msn.com, you can see that Google considers these two different urls. In order to correct this problem, MSN could redirect msn.com to www.msn.com with a 301 redirect, but instead they used a 302.

I’m sure MSN understands the problem behind using a 302 and may be using this as a way to highlight the issues Google has with canonical urls.

Hopefully Google will respond to this and fix the problem for all sites that have been affected – not just a big site like MSN.

Update: Looks like MSN is back to PR 9. Here’s what GoogleGuy said over at WebmasterWorld forums:

I think we decided to do a re-export of PageRank so that msn.com wouldn’t worry that should have more green pixels; I wouldn’t be surprised if a minor refresh of backlinks was included in that re-export.

I’m not 188% sure that’s what happened, but I noticed that www.msn.com returns a PR9-ish now, so I’m extrapolating my guesses here. Your comment matches what I would expect to see if that happened.